The possibility of someone else's trauma shouldn't infringe on my freedom to ride a bike without a helmet.
Drug use has one victim : the user. Time and time again it has been shown that legalization and cure are far more efficient and cost less to society but still many countries cling to the idea that beating up somebody who is down will magically solve the problem.
If you think the impact on a counterparty in a car accident should be taken into account, I would think family should be top-of-mind.
That has a much higher likelihood than my not-wearing-a-helmet affecting someone else but very few people would support alcohol prohibition.